1. Field of the Invention
The present invention relates to an image quality adjusting apparatus used for a digital copying machine, and more particularly to the image quality adjusting apparatus which is capable of treating color quality of an image copied on paper.
2. Description of the Related Art
The present inventor knows that some color copying machines have provided an image quality adjusting apparatus for adjusting color quality of an image copied on paper. As a representative related art of the image quality adjusting apparatus, the invention disclosed in the International Publication No. WO88/04503 may be referred. This image quality adjusting apparatus is arranged to have a unit for generating a first electric signal of a test image having predetermined patterns standing for some quality factors such as a color tone, a unit for printing the test image, a unit for generating a second electric signal from the printed image, and a unit for comparing the first electric signal with the second electric signal and adjusting a process parameter to reduce to a minimum the difference between the actual test image and the copied image.
Hence, the foregoing image quality adjusting apparatus has a capability of automatically adjusting quality of an image copied on paper by using the predetermined test image if the copying machine gradually degrades on time and disables to keep the initial quality on all the printed images because of changeable environmental conditions.
As mentioned above, such an image quality adjusting apparatus for a color copying machine uses the method of comparing a predetermined test image with its printed image on paper for adjusting the color quality of a printed image. If, therefore, the test image is different from the actual printed color image, the image quality adjusting apparatus cannot carry out fine adjustment of the color quality of the printed image.
In actual, the printed color image contains so many color tones like a half tone that a predetermined test image cannot stand for them rigorously. Hence, it is difficult to amend all these color tones only by securing reproducibility of slight patterns on the test image. It means that the use of the predetermined test image disadvantageously does not reach fine adjustment of the quality of the image copied on paper.